1. Field of the Invention
The present invention relates to an ultra low tension relax process and apparatus wherein a tension gate is incorporated into a relax zone in the production of yarn. In particular, the present invention relates to a relax zone wherein yarn is relaxed to control its shrinkage and a tension gate is employed to step wise increase the tension without decreasing the yarn instability. Yarn instability is characterized by lateral yarn movement (on the relax rolls, for example), yarn wrapping, and yarn breaking. The apparatus and process of the present invention has two immediate benefits, namely: 1) when used in the relax zone of a yarn production process, the relax can be significantly increased thereby decreasing the shrinkage of the yarn compared to conventional processes having no such tension gate, and 2) providing a step wise tension increase, compared with conventional apparatus, such that good yarn stability is achieved. Typical processes having a relax zone in yarn production are spin-drawing, draw-twisting, draw-winding, and draw-bulking processes.
2. Prior Art
FIG. 4 of U.S. Pat. No. 4,414,169 to McClary illustrates a typical spin-drawing process. The fibers are spun from a spinneret and subsequently drawn by a series of rolls. After drawing the yarn, conventionally there is a set of rolls being driven at a lower speed than the draw rolls, thereby creating a relax (low tension) zone. As illustrated by the examples, the windup speeds were roughly 2700 meters per minute. The resulting shrinkage measured at 175xc2x0 C. in air ranges from 4 to 9%.
The reason it was not possible to achieve very high levels of relax in a conventional spin-drawing process, is because at the higher levels of relax there is low yarn tension, which causes yarn wraps around the relax rolls to become very unstable and this often leads to yarn breakage. To provide good yarn stability and prevent yarn breakage, a minimum threadline tension is required. It is not possible to operate below this minimum tension, and thus high levels of relax are not possible with a conventional spin-drawing process. The reason multiple wraps are employed on the relax rolls is to insure that the yarn is moving at a fixed speed as determined by the relax rolls (constant yarn speed is required for the winder to maintain good operation), and to isolate the tension on the winder (this is required to obtain a good package).
U.S. Pat. No. 5,925,460 to Hofs et al discloses, in a spin-drawing process, drawn yarn shrinkages measured at 177xc2x0 C. ranging from 3.7 to 5.9%. Hofs et al disclose high wind-up speeds in excess of 6000 meters per minute.
U.S. Pat. No. 4,096,226 to Martin et al discloses a spin-drawing-texturizing process for polyamide yarn. The texturizing device (also know as draw-bulking) has an overfeed of 10-50%.
U.S. Pat. No. 4,491,657 to Saito et al discloses a high modulus, low shrink tire yarn. Tables 1 and 2 generally show that as process speed increases, the shrinkage decreases.
U.S. Pat. No. 4,973,657 to Thaler discloses a high modulus, low shrink tire yarn. The table shows that as the residence heating time increases, the shrinkage decreases (compare Example 5 with 6). It also shows that as the temperature decreases, the shrinkage increases (compare Example 4 with 5).
U.S. Pat. No. 5,227,858 to Neal discloses an industrial yarn and shows that as the temperature increases, the shrinkage decreases. This patent also teaches the advantages of employing rolls having a special surface for contacting the yarn.
U.S. Pat. No. 5,066,439 to Nishikawa et al teaches a continuous spin draw process for making polyester yarn, whereby a commingler is introduced between the second draw rolls and the relax rolls just prior to wind-up. In column 4, line 20 Nishikawa et al state that the relaxation ratio can be enhanced greatly by applying the commingling treatment to the yarn between the second draw rolls 6 and the relaxation rolls 10. More specifically, in column 6 line 19-22 it states that the relaxation was done at a ratio of 5 to 12%.
The two tables set forth below summarize the data in Examples 1 and 2 of Nishikawa et al. In particular, Example 1 data shows drawing speeds of about 3000 meters per minute and with relaxation ratios varying from 5 to 12%. The stability of the yarn with the heaters on and off and the commingler (at 28.44 psi) being on and off is shown. Example 1 indicates that whether the heater and commingler are on or off, good stability (no breaks) can result. Example 2 shows drawing speeds of 4500 meters per minute with a constant relax ratio in each instance of 8%. Example 2 demonstrates that when the commingler is operating at approximately 42.66 psi, good stability can only be achieved when the heater is on. Example 2 clearly shows that the improvement in stability is due to the heater, and not the commingler. In other words there is no data showing that commingling alone yields improved stability.
The present invention is an ultra low tension relax process and apparatus positioned within the relax zone of a yarn production process such as a spin-drawing process, a draw-twisting process, draw-winding, or a draw-bulking yarn process. The concept of the present invention is to introduce a tension gate into the relax zone found in any of these processes. The purpose of the tension gate is to enable very high relax levels with ultra low tension such that low shrinkage of the yarn is achieved. Additionally the tension gate provides for significantly improved stability in that no yarn wrapping and no yarn breakage occur when using the tension gate of the present invention in a conventional relax zone. With respect to a conventional spin-drawing process, for example, the tension gate maintains the minimum level of tension necessary for the yarn arriving at the relax rolls, thus preventing breakage, while permitting the yarn to relax between the draw rolls and the tension gate. The tension gate permits yarn relax to exist before the tension gate, while creating an increase in the yarn tension after the tension gate so that yarn instability improves on the wraps on the relax rolls, so that no yarn breakage occurs.
With drawing speeds of less than about 2500 meters per minute, yarn stability is not a major problem. At such speeds good relax percentages can be achieved and yarn stability or breakage is virtually nil. However, as process speeds increase, achieving a high relax ratio becomes more difficult because yarn tension falls as relax is increased, and instability results thereby incurring yarn wrap and breakage. Additionally, trying to achieve increased relaxation in a conventional process, to reduce overall shrinkage creates yarn instability (the yarn traverses from side to side on the relax rolls) resulting in breaks, and/or a poor mechanical quality due to the yarn abrasion from traversing back and forth across the rolls.
The tension gate of the present invention partitions a relax zone in a conventional process into a relax zone and a small stretching zone. Different devices, when positioned in a conventional relax zone can create a partition. Tension gates can be created by applying drag to the yarn, by means of air drag, liquid drag, or drag produced by pulling the yarn over a solid surface. Air drag can be applied to the yarn by employing one or more interminglers or a counter-current air-flow device, for example. Liquid drag can be introduced by employing one or more finish applicators (a finish applicators is a device well known to those in the textile industry, as it applies a liquid finish or coating to the yarn), or by drawing the yarn through a pool of liquid, for example. Solid surface drag can be introduced by contacting the yarn with one or more solid surfaces (like rolls) over or around which the yarn traverses, but because the yarn does not have multiple wraps on a roll, traversing yarn on the tension gate device is not a problem, and does not cause yarn breakage.
In the broadest sense, the present invention relates to a yarn making process having a relax zone for partitioning the tension on the yarn, comprising the step of providing a tension gate in the relax zone which creates a tension differential on the yarn of at least 5 milligrams per denier (mg/d).
Also in the broadest sense, the present invention relates to a tension gate for increasing the tension on yarn with no yarn breakage, comprising employing one or more air, liquid or solid surface drag devices or a combination of these having a yarn tension differential (the yarn tension exiting the tension gate minus the yarn tension entering the tension gate) of at least 5 mg per denier.